Communication devices, such as cell phones and smart phones adopting wireless 2G/3G/4G (LTE, long term evolution) mobile telecommunication standard(s), have become prevailing and essential for contemporary information society. To successfully establish mobile communication, communication devices need to be calibrated.
For example, while a communication device receives downlink signals (e.g., from base stations or node B's), it is expected to correctly measure received downlink power over a frequency range, e.g., a band/channel, or a sub-band/sub-channel as a portion of a band/channel. However, communication device unavoidably suffers non-uniform power measurement accuracy over wide frequency range. Thus, gain calibration is applied to communication device to understand power measurement accuracy over the frequency range. As mobile telecommunication evolves for higher data throughput, the aforementioned frequency range becomes much wider. For example, the frequency range may be 60 MHz for LTE.
To evaluate power measurement accuracy over a frequency range, the frequency range is resolved to several frequencies; e.g., a frequency range of 60 MHz may be resolved to 10 frequencies by a 6 MHz separation between every two adjacent frequencies. Conventionally, gain calibration is performed by: from a test equipment, supplying a single CW (continuous wave) tone of a first resolving frequency to the communication device to evaluate power measurement accuracy at the first resolving frequency, and supplying a single CW tone of a second resolving frequency to the communication device to evaluate power measurement accuracy at the second resolving frequency, and so forth. Accordingly, if the frequency range is resolved to a number K of frequencies, then the convention gain calibration needs K iterations.
In addition, communication device is capable of providing several gain modes, so received signal can be amplified by different gains respectively in different gain modes. Because communication device may utilize either one of the gain modes to receive signals, power measurement accuracies respectively in different gain modes need to be calibrated. That is, to cover a number N of gain modes and a number K of frequencies resolving the frequency range, the convention gain calibration takes N*K iterations (pts). Hence, the convention gain calibration is inefficient because so many iterations consume much calibration resources, including time and cost.